1. Field of the Invention
The invention relates to active, non-intrusive measurement of the mass flow rate of a gas flow, such as in gas turbine engines. Mass flow rate is commonly used as an indicator of performance of gas turbine engines. Such engines include, by way of example, industrial gas turbine (IGT) engines, other types of stationary gas turbine, marine, aero and other vehicular gas turbine engines. More particularly, embodiments of mass flow rate measurement methods and apparatus disclosed herein utilize non-intrusive acoustic transceivers for velocity and temperature determinations along lines of sound within the gas flow. In embodiments disclosed herein, the temperature and velocity determinations are used in computing an overall mass flow rate for the engine. The computed mass flow rate is used for gas turbine engine monitoring, control and performance evaluation.
2. Description of the Prior Art
Combustion turbines, such as gas turbine engines for any end use application, generally comprise a compressor section, a combustor section, a turbine section and an exhaust section. In operation, the compressor section inducts and compresses ambient air. The combustor section generally may include a plurality of combustors for receiving the compressed air and mixing it with fuel to form a fuel/air mixture. The fuel/air mixture is combusted by each of the combustors to form a hot working gas that may be routed to the turbine section where it is expanded through alternating rows of stationary airfoils and rotating airfoils and used to generate power that can drive a rotor. The expanding gas exiting the turbine section can be exhausted from the engine via the exhaust section.
Combustion anomalies, such as flame flashback, have been known to occur in combustion sections of gas turbine engines. Flame flashback is a localized phenomenon that may be caused when a turbulent burning velocity of the air and fuel mixture exceeds an axial flow velocity in the combustor assembly, thus causing a flame to anchor onto one or more components in/around the combustor assembly, such as a liner disposed around the combustion chamber. The anchored flame may burn through the components if a flashback condition remains for extended periods of time without correction thereof. Thus, flame flashback and/or other combustion anomalies may cause undesirable damage and possibly even destruction of combustion engine components, such that repair or replacement of such components may become necessary.
The fuel/air mixture at the individual combustors is controlled during operation of the engine to maintain one or more operating characteristics within a predetermined range, such as, for example, to maintain a desired efficiency and/or power output, control pollutant levels, prevent pressure oscillations and prevent flameouts. In a known type of control arrangement, a bulk turbine exhaust temperature may also be monitored as a parameter that may be used to monitor the operating condition of the engine. For example, a controller may monitor a measured turbine exhaust temperature, and a measured change in temperature at the exhaust may result in the controller changing an operating condition of the engine. In other known types of control arrangements discrete pitot-static or multi hole pressure probes are utilized to determine gas flow velocity at specific locations, but grid arrays of such probes disrupt gas flow and introduce measurement errors. Due to such gas flow disruptions, grid arrays, when employed, have limited numbers of widely spaced probes, which provide relatively coarse gas flow velocity distribution and profile information.
At present, there are several different types of sensors and sensing systems that are being used in the industry for monitoring combustion and maintaining stability of the combustion process for engine protection. For example, dynamic pressure sensors are being used for combustion stability and resonance control. Passive visual (optical visible light and/or infrared spectrum) sensors, ion sensors and Geiger Mueller detectors are used to detect flame on/off in the combustor, while thermocouples are being used for flashback detection. With respect to known combustion gas flow velocity (u) monitoring methods, pitot-static and multi hole pressure probes utilize differential pressure techniques, hot wire probes utilize thermal anemometry techniques, while Laser Doppler and Particle Image Velocimetry systems utilize optical techniques to characterize gas flow velocities. Differential pressure and thermal anemometry instruments are intrusive point measurement devices that disturb local gas flow around the instruments. Laser Doppler and Particle Image Velocimetry instruments respectively provide non-intrusive point and 2- or 3-dimensional non-intrusive gas flow velocity measurement although they both require particle seeding of the flow. In addition, sophisticated laser based measurements such as Filtered Rayleigh Scattering (FRS) and other such laser spectroscopy based techniques have been deployed to measure gas velocity. However, these techniques are more complex than intrusive differential pressure or thermal anemometry instruments and require more specialized training to implement in monitoring systems. Moreover, most optical techniques for velocity are geared towards laboratory environments rather than in operative engines at power plant field sites. With respect to temperature (T) monitoring techniques, known Raman Spectroscopy, Laser Induced Fluorescence (for both u and T monitoring), and Coherent Anti-Stokes Raman Spectroscopy (CARS) (for both u and T monitoring) instrumentation systems are also intended for laboratory environments, rather than for field use in fossil power generation equipment. Tunable Diode Laser Absorption Spectroscopy (TDLAS) instrumentation is used in some industrial power generation field applications, such as for temperature measurement in boilers but that instrumentation is extremely costly: approximately US $500,000 per system. Other types of temperature measurement and combustion anomaly detection systems have had greater acceptance in power generation industry field applications.
Particularly, U.S. Pat. No. 7,853,433 detects and classifies combustion anomalies by sampling and subsequent wavelet analysis of combustor thermoacoustic oscillations representative of combustion conditions with sensors, such as dynamic pressure sensors, accelerometers, high temperature microphones, optical sensors and/or ionic sensors. United States Publication No. US2012/0150413 utilizes acoustic pyrometry in an IGT exhaust system to determine upstream bulk temperature within one or more of the engine's combustors. Acoustic signals are transmitted from acoustic transmitters and are received by a plurality of acoustic receivers. Each acoustic signal defines a distinct line-of-sound path between a corresponding transmitter and receiver pair. Transmitted signal time-of-flight is determined and processed to determine a path temperature. Multiple path temperatures can be combined and processed to determine bulk temperature at the measurement site. The determined path or bulk temperature or both can be utilized to correlate upstream temperature in the combustor. Co-pending U.S. utility patent application No. Ser. No. 13/804,132 calculates bulk temperature within a combustor, using a so-called dominant mode approach, by identifying an acoustic frequency at a first location in the engine upstream from the turbine (such as in the combustor) and using the frequency for determining a first bulk temperature value that is directly proportional to the acoustic frequency and a calculated constant value. A calibration second temperature of the working gas is determined in a second location in the engine, such as the engine exhaust. A back calculation is performed with the calibration second temperature to determine a temperature value for the working gas at the first location. The first temperature value is compared to the back calculated temperature value to change the calculated constant value to a recalculated constant value. Subsequent first temperature values at the combustor may be determined based on the recalculated constant value.
Accurate performance evaluation of gas turbine engines designed for power generation is a major challenge faced by both OEMs and end users. OEMs use performance data primarily to validate new engine designs, while end users need performance data to determine their produced power. Mass flow rate through a gas turbine engine is an important element of performance measurement.
Currently, a combination of intrusive probes and pressure taps provide approximate temperature and velocity information that is used to estimate the performance characteristics of a gas turbine engine. The estimates rely on broad assumptions regarding temperature and flow profiles across the gas flow field. Such velocity and flow information have a high level of uncertainty due to non-uniformities of the gas flow field that are not properly captured in the probe and pressure tap measurements. In addition, measurements suffer from inaccuracies due to the intrusive nature of the techniques used, in which the measured flow is disrupted.
In laboratory environment, under tightly controlled boundary conditions paired with clean room conditions, various optical methods are being successfully used to measure flow and temperature non-intrusively. This is primarily the case for wind tunnels and test-rigs or tests under simulated environments. Under realistic engine conditions at a test engine or at a plant, however, these techniques are unusable at their current state of maturity. Even if utilized, they do not provide sufficiently accurate flow measurement data for use in performance measurement.
Thus, a need exists in the art for an accurate mass flow rate monitoring system that maps actual gas density and gas velocity measurements within a measurement volume of the flow path to account for dynamic flow field variations.
An additional need exists for an active mass flow rate monitoring system in which temperature and velocity measurements are made non-intrusively, thus not disturbing the measured flow field.
An additional need exists for an active mass flow rate monitoring system that shares sensors commonly used with turbine monitoring and control systems, so that active mass flow rate monitoring can be integrated within the monitoring and control system.
Another need exists for an accurate mass flow rate monitoring system that computes a mass flow value over time to compensate for an unsteady flow profile as well as short term inaccuracies and variability in the monitoring system.
An additional need exists for an integrated gas turbine engine monitoring and control system for measuring mass flow rate and other parameters, and for providing performance information to a turbine controller in a feedback loop, sharing common sensors and, if desired, a common controller.